Stable Operation Period Research Articles

Transient Electronics as Sustainable Systems: From Fundamentals to Applications

AbstractThe unique attribute of transient technology is that it promotes the potential for the design and implementation of sustainable systems through their capability to fully or partially disintegrate after a predefined period of stable operation. Transient electronics have a wide range of potential applications as biomedical implants, environmental sensors, and hardware‐secured devices. Controlled disintegration of such systems without the need for harsh solvents is a step toward realizing green and sustainable electronics. In this short review, recent progress in the development of transient electronics is studied. First, an overview of the transient materials, both the substrate and electronic component, is described. Second, the mechanisms under which transiency occurs, including aqueous dissolution and thermal degradation, are reported. Third, manufacturing techniques for the fabrication of transient electronics are reviewed. And last, various transient electronic devices and their applications are discussed.

Degradation Behavior, Biocompatibility, Electrochemical Performance, and Circularity Potential of Transient Batteries.

Transient technology seeks the development of materials, devices, or systems that undergo controlled degradation processes after a stable operation period, leaving behind harmless residues. To enable externally powered fully transient devices operating for longer periods compared to passive devices, transient batteries are needed. Albeit transient batteries are initially intended for biomedical applications, they represent an effective solution to circumvent the current contaminant leakage into the environment. Transient technology enables a more efficient recycling as it enhances material retrieval rates, limiting both human and environmental exposures to the hazardous pollutants present in conventional batteries. Little efforts are focused to catalog and understand the degradation characteristics of transient batteries. As the energy field is a property‐driven science, not only electrochemical performance but also their degradation behavior plays a pivotal role in defining the specific end‐use applications. The state‐of‐the‐art transient batteries are critically reviewed with special emphasis on the degradation mechanisms, transiency time, and biocompatibility of the released degradation products. The potential of transient batteries to change the current paradigm that considers batteries as harmful waste is highlighted. Overall, transient batteries are ready for takeoff and hold a promising future to be a frontrunner in the uptake of circular economy concepts.

Sustainability and tool wear of titanium alloy thread cutting in dry and cryogenic conditions

The article is devoted to the study of the effect of cryogenic cooling on the tool wear in thread turning tests. The tool wear and its influence on the thread accuracy were investigated. Two different grades of titanium alloys were used for comparative purposes. The excellent performance characteristics of titanium alloys pose machining problems, causing high unit forces at the edge of the tool leading to chipping and premature tool failure. In turn, the low thermal conductivity of pure titanium affects the heat distribution in the cutting zone. The heat is not absorbed by the material being machined but accumulates in the tool, causing an increase in diffusion and chemical wear. The results of cutting tests using liquid nitrogen showed lower values of wear on the major and minor tool flank. The edge reduction of the tool was also significantly less during cryogenic machining. The analysis of the formation of wear marks and the blade wear mechanisms was carried out for the tool rake face. The tests were carried out using the SEM method and confirmed by EDS analyses. In order to compare the course of tool wear over time, a mathematical model was developed, which results from the course of phenomena during cutting. It consists of two complementary equations. The first equation is characteristic for the first cutting phase and results from the loads imposed on the blade and aims at thermodynamic equilibrium. It is a period of stable tool operation and constant wear intensity. The second equation concerns crossing the equilibrium point followed by the process of accumulation of elementary wear phenomena. These phenomena accumulate until the blade is completely worn-out. The use of blade wear development models to determine the expected blade life allowed to confirm the beneficial effect of cryogenic cooling on the course of the blade wear process when cutting threads for two different titanium alloys.

Simultaneous Removal of Trivalent Arsenic and Nitrate Using Microbial Fuel Cells

A rectangular double chamber with trivalent arsenic as the electron donor of the biological anode was constructed by microbial fuel cells (MFC), and the feasibility of the MFC simultaneous degradation of trivalent arsenic and nitrate was studied. Experimental results show that the co-matrix-coupled MFC reactor oxidizes trivalent arsenic in an anode chamber and degrades nitrate in the cathode chamber. The removal rate of trivalent arsenic is about 63.35%, and the degradation rate of nitrate is about 55.95% during the complete and stable operation period. MFC can continuously output electric energy, and the maximum output voltage is 388 mV. We compared and analyzed the main functional microflora of biofilm microorganisms in an anode chamber. In the long-term arsenic-polluted environment, the activity of Acinetobacter, Pseudomonas bacteria with arsenic resistance, was improved. It is inferred that a fraction of trivalent arsenic was oxidized to pentavalent arsenic by electrode-attached microorganisms. While remaining trivalent, arsenic was taken up by the suspended bacterial biomass and converted into stable arsenide. The results of this study have theoretical reference value for the expansion of the MFC application scope.

Treatment of high-salt oil produced water based on constructed wetland technology—A case study of a costal oilfield

Aiming at the treatment of large volume of oil produced wastewater, the combined technology based on constructed wetland was applied for produced water treatment in a costal oil field. During the stable operation period, the treatment system maintained removal efficiency of 50.2% for chemical oxygen demand (COD), 100% for oil and 85.1% for ammonium nitrogen (NH3-N) under the gradient increase of salinity along the process. Meanwhile, this system has a good ability to adapt the influent fluctuation. When the oil in the influent fluctuated greatly between 11 mg/L to 147 mg/L, the effluent water quality remained stable. The treated water met the national discharge standard for water pollutants from the oilfield industry and can be used for the saline alkali beach wetland as supplement water.

Equipment for pulsed gas-and-chemical regeneration of water wells

The development of new methods for the regeneration and recovery of specific flow rate of water intake wells is an urgent task. Based on many years of the experience in well operation, it has been proved that all wells eventually need to be repaired. The main reason for such work is the chemical clogging of the filter and filter zone with different chemical compounds. The average stable operation period of new wells is 2–4 years. Better cleaning of filters and filter zones in water intake wells is achieved using the combination of hydraulic, impulse and vibration attacks with subsequent or concurrent chemical treatment. At this date, none of the integrated approaches enjoys wide application due to some disadvantages. At the Belarusian National Technical University, the pulse-and-chemical regeneration equipment has been designed for water intake wells. The technology involves electrolysis-induced explosion of a hydrogen–oxygen mixture at the well mouth on ground surface, feed of the mixture to a working chamber in the well filter, filling of a chemical reagent in the filter treatment zone and explosion of the reagent medium. The equipment has successfully passed laboratory and field tests.

An Inter-Comparison of Dynamic, Fully Coupled, Electro-Mechanical, Models of Tidal Turbines

Production of electricity using hydrokinetic tidal turbines has many challenges that must be overcome to ensure reliable, economic and practical solutions. Kinetic energy from flowing water is converted to electricity by a system comprising diverse mechanical and electrical components from the rotor blades up to the electricity grid. To date these have often been modelled using simulations of independent systems, lacking bi-directional, real-time, coupling. This approach leads to critical effects being missed. Turbulence in the flow, results in large velocity fluctuations around the blades, causing rapid variation in the shaft torque and generator speed, and consequently in the voltage seen by the power electronics and so compromising the export power quality. Conversely, grid frequency and voltage changes can also cause the generator speed to change, resulting in changes to the shaft speed and torque and consequently changes to the hydrodynamics acting on the blades. Clearly, fully integrated, bi-directional, models are needed. Here we present two fully coupled models which use different approaches to model the hydrodynamics of rotor blades. The first model uses the Blade Element Momentum Theory (BEMT), resulting in an efficient tool for turbine designers. The second model also uses BEMT, combines this with an actuator line model of the blades coupled to an unsteady computational fluid dynamics simulation by OpenFOAM (CFD/BEMT). Each model is coupled to an OpenModelica model of the electro-mechanical system by an energy balance to compute the shaft speed. Each coupled system simulates the performance of a 1.2 m diameter, three-bladed horizontal axis tidal turbine tested in the University of Edinburgh FloWave Ocean Energy Research Facility. The turbulent flow around the blades and the mechanical-electrical variables during the stable period of operation are analysed. Time series and tabulated average values of thrust, torque, power, and rotational speed, as well as, electrical variables of generator power, electromagnetic torque, voltage and current are presented for the coupled system simulation. The relationship between the mechanical and electrical variables and the results from both tidal turbine approaches are discussed. Our comparison shows that while the BEMT model provides an effective design tool (leading to slightly more conservative designs), the CFD/BEMT simulations show the turbulence influence in the mechanical and electrical variables which can be especially important in assessing an additional source of stresses in the whole electro-mechanical system (though at an increased computational cost).

Performance and economic analyses of a combined bioreactor for treating odors, volatile organic compounds, and aerosols from a landfill site

A full-scale combined bioreactor with a biological aeration zone (BAZ) and a biological filtration zone (BFZ) was adopted to treat odors, volatile organic compounds (VOCs), and aerosols emitted from a landfill site. The BAZ mainly relies on suspended microorganisms that degrade substances with high water solubility, while the BFZ is divided into an acidic biofiltration unit (ABU) and a neutral biofiltration unit (NBU) to further remove remaining contaminants. Average removal efficiencies (REs) of 97.21%, 98.89%, 92.44%, 73.12%, and 81.89% for H2S, NH3, VOCs, culturable bacteria, and fungi, respectively, were achieved during the stable operation period. In particular, the concentrations of water-soluble ions (WSIs), including SO42−, NO2−, NO3−, and Cl− in aerosols, were significantly reduced by the combined bioreactor. The REs and degradation product characteristics for the odors, VOCs, and aerosols in the BAZ and BFZ were different due to different dominant microorganisms. In addition, the economic cost of the combined bioreactor was analyzed considering investment cost, operating cost, and packing material replacement cost, and a sensitivity analysis was performed to determine economically-sensitive parameters. This study clearly demonstrates the low cost and effectiveness of the combined bioreactor to treat exhaust gases containing odors, VOCs, and aerosols from a landfill site.

Removal of bisphenol A by waste zero-valent iron regulating microbial community in sequencing batch biofilm reactor

The removal of bisphenol A (BPA) by waste zero-valent iron (ZVI) regulating microbial community in sequencing batch biofilm reactor (SBBR) was investigated. Compared with SBBR-BPA, the acclimation time of microorganisms in the presence of waste ZVI and BPA (SBBR-ZVI+BPA) decreased from 56 d to 49 d. During stable operation period, BPA was removed completely at 150th min and 100th min in the SBBR-BPA and SBBR-ZVI+BPA, respectively. The optimal initial pH and BPA concentration in the SBBRs were respectively 8.0 and 10 mg/L. The composition and content analysis of extracellular polymeric substances (EPS) using fluorescence spectrometer showed that the yield of EPS was enhanced by the addition of ZVI. The analysis of microbial community structure in the SBBRs using Illumina Miseq sequencing method indicated that the indexes of ACE, Chao1 and Shannon were higher and Simpson index was lower in the SBBR-ZVI+BPA. Moreover, the abundance of BPA biodegradation strains was increased in the presence of ZVI. This study provided a promising method with low cost of effectively removing BPA from wastewater.

Comparative evaluation on the utilization of applied electrical potential in a conductive granule packed biotrickling filter for continuous abatement of xylene: Performance, limitation, and microbial community

This study investigates the use of electrically conductive granules as packing material in biotrickling filter (BTF) systems as to provide insights on the specific microbial abundance and functions during the treatment of xylene-containing waste gas. In addition, the effect of applied potential on attached biofilm on conductive granules during xylene degradation was briefly investigated. During stable operation period, the conductive granules packed BTF achieved reactor performance of no less than 80% with a maximum EC of 137.7 g/m3 h. Under applied potential of 1V, the BTF system showed deterioration of xylene removal by ranging from 21 to 76%, which also affected the distribution and relative abundance of the major microorganisms such as Xanthobacter, Acidovorax, Rhodococcus, Hydrogenophaga, Arthrobacter, Brevundimonas, Pseudoxanthomonas, Devosia, Shinella, Sphingobium, Dokdonella, Pseudomonas and Bosea. The acclimation of applied potential led to the enrichment of autotrophic bacteria and strains, which are correlated to improved nitrogen cycling. In general, applying electrical potential is feasible to shape the microbiological structure of biofilms to selectively adjust their biochemical functions.

Two birds with one stone: Simultaneous improvement of biofilm formation and nitrogen transformation in MBBR treating high ammonia nitrogen wastewater via exogenous N-acyl homoserine lactones

Moving bed biofilm reactor (MBBR) is facing the challenges of slow start-up and poor treatment performance when treating high ammonia nitrogen wastewater, especially at low temperature. Exogenous N-acyl homoserine lactones (AHLs) were proposed to improve the biofilm formation and pollutant removal simultaneously for the first time. The effects of 100 nM exogenous C6-HSL and C8-HSL on the distribution of AHLs, reactor performance, biofilm characteristics and microbial community structure were systematically investigated in six lab-scale MBBRs treating wastewater with 200 mg/L ammonia nitrogen at 25 °C and 5 °C. Results showed that exogenous AHLs exhibited more significant influences during the stable operation period rather than the start-up of MBBR. Biofilm growth and EPS secretion were significantly promoted by C8-HSL (p < 0.05) while inhibited by C6-HSL at 25 °C, however, the results were opposite at 5 °C. Denitrogenation-related enzyme activities and function genes, and abundances of bacteria possessing quorum sensing and pollutants degradation ability, were heightened by exogenous AHLs (p < 0.05), thus enhancing biofilm formation and pollutants removal at room and low temperature. This study inspired a feasible strategy towards synchronous enhancement of biofilm growth and performance of MBBR treating high ammonia nitrogen wastewater through exogenous AHLs.

Undesirable effects of exogenous N-acyl homoserine lactones on moving bed biofilm reactor treating medium-strength synthetic wastewater

Exogenous AHLs are gradually reported to facilitate biofilm growth, however, whether they play a universal role in promoting biofilm formation and pollutants removal remains to be investigated. The pollutant removal, biofilm properties, microbial community and the distribution of AHLs were investigated in three lab-scale MBBRs by continuous dosing 100 nM N-Hexanoyl-L-homoserine lactone (C6-HSL) and N-Octanoyl-L-homoserine lactone (C8-HSL) in synthetic wastewater under normal nutrition (40 mg/L NH4+-N with C/N = 20). Results showed that adding AHLs didn't affect organics removal and exogenous C6-HSL even significantly suppressed NH4+-N removal by 0.44–20.29% after 16 days (p < 0.05). The introduction of AHLs both facilitated biofilm growth and extracellular polymeric substances secretion while suppressed ATP production especially during the stable operation period, with 48.96% by C6-HSL (p < 0.05) and 27.25% by C8-HSL, respectively. Exogenous AHLs inhibited the proliferation of Chryseobacterium, resulting in improvement in biofilm growth and it probably mediated ATP synthesis through regulating the release of 3OHC12-HSL in aqueous phase. Organics removal and biofilm growth were mainly attributed to the combined actions of multitudinous AHLs in biofilm phase rather than that in aqueous phase. The counterintuitive conclusions obtained in this study highlighted the importance of legitimately applying exogenous AHLs to accelerate biofilm formation and the start-up of MBBR in wastewater treatment.

Effect of dilutional anemia that can be treated with only one unit of red blood cell transfusion on tissue oxygenation in cardiac surgery patients

Background/aim Cardiac surgery, especially in the presence of cardiopulmonary bypass (CPB), is associated with an inflammatory reaction that may promote microcirculatory alterations, in addition to the general impact on system hemodynamics. Anemia and transfusion make patients more susceptible to the deleterious effects of CPB. In this study, it was aimed to evaluate the effect of dilutional anemia, which is caused by CPB and can be treated with 1–2 units of red blood cell (RBC) transfusion, on global tissue oxygenation parameters in cardiac surgery patients.Materials and methods This prospective observational study comprised 127 patients who had a relatively stable operation period without any major anesthetic or surgical complications (e.g., operation duration >5 h, bleeding or hemodilution requiring more than 1–2 units of RBCs, or unstable hemodynamics, requiring inotropic support of more than 5 µg/kg/min dopamine). Patients were observationally divided into two groups: minimally transfused (Group Tr) and nontransfused (Group NTr). Global tissue oxygenation parameters were evaluated after anesthesia induction (T1) and at the end of the operation (T3) and compared between the groups.Results Group Tr consisted of patients who had significantly lower preoperative hemoglobin values than Group NTr patients. The dilutional anemia of all Group Tr patients could be corrected with 1 unit of RBCs. The lactate levels at T3, increment rates of lactate, and venoarterial carbon dioxide pressure difference (ΔpCO2) levels [(T3 – T1) : T1] in Group Tr were significantly higher than those in Group NTr.Conclusion Dilutional anemia as a result of CPB mostly occurs in patients with borderline preoperative hemoglobin concentrations and its correction with RBC transfusion does not normalize the degree of microcirculatory and oxygenation problems, which the patients are already prone to because of the nature of CPB. Preventing dilutional anemia and transfusion, especially in patients with preoperative borderline hemoglobin levels, may therefore reduce the burden of impaired microcirculation-associated organ failure in on-pump cardiac surgery.

Start-up and Performance Optimization of a CANON Pilot Reactor

A completely autotrophic nitrogen removal over nitrite (CANON) reactor was established by seeding ordinary activated sludge with reject water as the influent at (30±3)℃ from a sewage treatment plant in Qingdao. To solve bacterial loss and optimize reactor performance, a suspension of biological carriers was added to the CANON reactor. The result showed that the reactor was successfully started 130 days later. The total nitrogen removal load was up to 0.03 kg·(m3·d)-1, and the average variation ratio of nitrate and ammonia (RNaA) was 0.09, which was close to theoretical value 0.11. The CANON active sludge reactor ran for 300 days. During the stable operation period, the total nitrogen removal rate was stable at 0.20 kg·(m3·d)-1. Red granular sludge was mixed with the effluent of the system, and the particle size of granular sludge was between 1 and 3 mm. The suspension carriers were added to the CANON reactor with a filling rate of 30%. The fillers added to the moving bed biofilm reactor (MBBR) were mature fillers in the nitrifying reactor of the laboratory. The accumulation rate of nitrification was greater than 95%, and the ammonia-oxidized surface load reached 2.0 g·(m2·d)-1. After 30 days of operation and culturing, the system was successfully converted to a pure membrane system, and the biofilm on the surface of the carrier turned pale red. The total nitrogen removal load was up to 0.17 kg·(m3·d)-1. The average RNaA was 0.14, which was slightly higher than the theoretical value of 0.11. This suggested that the CANON sludge adapted to the environment in the MBBR and began to enter a stable stage. The CANON-MBBR ran for 200 days. During the stable operation period, the total nitrogen removal rate was stable at 1.15 kg·(m3·d)-1. The biofilm was bright brick red with a thickness of 150-250 μm. MLSS and MLVSS on the carriers were approximately 10200 mg·m-2 and 9000 mg·m-2, respectively, and the total biomass in the system was approximately 1.5 kg. Through high-throughput sequencing, AOB and AnAOB were found to be the dominant bacteria species on the suspension carrier, with a relative abundance of 26.24% and 30.08%, respectively, and nitrate oxidizing bacteria were successfully suppressed. The above results showed that CANON-MBBR with high-density polyethylene filler as the suspension carrier had good nitrogen-removal efficiency and was conducive to the stable operation of the autotrophic nitrogen removal process.

Simultaneous removal of nitric oxide and sulfur dioxide in a biofilter under micro-oxygen thermophilic conditions: Removal performance, competitive relationship and bacterial community structure

The efficiency of a biofilter to simultaneously remove nitric oxide (NO) and sulfur dioxide (SO2) was investigated under thermophilic (48 ± 2 °C) micro-oxygen (3 vol%) conditions. After the start-up stage (Days 0–14), the stable operation period was divided into three stages. SO2 inlet concentration remained 500 mg/m3, NO inlet concentrations were 300 mg/m3 (Days 15–40), 500 mg/m3 (Days 41–70) and 700 mg/m3 (Days 71–100). In each stable stage, the removal efficiency of NO and SO2 exceeded 90%, the maximum removal rates of NO and SO2 were 98.08% and 99.61%, respectively. The final products of SO2 were mostly sulphur. Nitrate-reducing bacteria inhibited sulphate-reducing bacteria. Illumina high-throughput sequencing confirmed that the relative abundance of nitrate-reducing bacteria was positively correlated with NO removal efficiency, the relative abundance of sulphate-reducing bacteria was related to the conversion rate of sulphur.

Analysis of Wastewater Membrane Pollutants in Joint Station and Research on Biological Control Technology

In view of the serious membrane pollution and short stable operation period of the existing heavy oil wastewater treatment process in a combined station of an oil field, the organic pollution is determined to be the main cause of the membrane pollution on the basis of the analysis of the wastewater quality and membrane pollutants. In view of the characteristic pollutants in heavy oil wastewater, the efficient degrading bacteria were screened by restrictive culture technology, and the strains were identified as Pseudomonas and Bacillus. The effects of environmental conditions on the growth of bacteria and the degradation of heavy oil by bacteria were investigated. In the existing process, biological treatment unit was added, simulation process was established, and long-term operation experiment was carried out. The results show that after biological treatment, the oil content of wastewater is less than 1 mg/L, COD is less than 100 mg/L, suspended matter is less than 1 mg/L, and the median particle size is 0.92 um, which is better than the first kind of water injection index (SY/T 5329-2012). Biological treatment effectively degraded organic pollutants in heavy oil wastewater and delayed membrane fouling. The loss rate of membrane flux was less than 15%. The microscopic morphology of membrane surface also showed that membrane fouling was effectively suppressed.

Laser Sintering of Zn Microparticles and Its Application in Printable Biodegradable Electronics

AbstractThe rapid expansion of electronic technology and short lifespan of consumer devices create a huge amount of electronic waste. The disposal of discarded devices represents a serious environmental challenge. Biodegradable devices are able to decompose into benign components after a period of stable operation during its service life, which represents a potential solution to reduce the environmental footprint of electronic technology. The widespread applications of biodegradable electronics are still hampered by the lack of facile manufacturing approach for high quality devices. Here, a laser sintering technique to weld naturally oxidized Zn microparticles into biodegradable conductors is reported. The sintering process is carried out under ambient conditions and compatible with various biodegradable substrates. A low‐cost fabrication procedure involving stencil printing and laser treatment is established to create conductive features with excellent conductivity and mechanical durability. The practical suitability of printed Zn conductor is demonstrated by fabricating near‐field communication tags, which are flexible and fully functional with the transient behavior modulated by the choice of packaging materials. The printed biodegradable conductor may find potential applications in eco‐friendly sensors, transient printed circuit boards, and implantable medical devices.

Simultaneous sludge degradation, desalination and bioelectricity generation in two-phase microbial desalination cells

The invention of solid phase bioelectrochemical systems (SPBESs) provides a promising method for synchronous dehydrated sludge compost, desalination and bioelectricity generation. However, low power density and anodic salinization are common problems in SPBESs. A two-phase microbial desalination cell (TPMDC) could achieve simultaneous desalination of saline solution and dehydrated sludge by adding concentration chambers. Experimental results indicated that the Dsalt in 3 d for different concentration saline solutions were 6.00 ± 0.05% (35 g L−1), 10.75 ± 0.76% (10 g L−1), and 19.80 ± 0.64% (2 g L−1) respectively during the stable operation period of TPMDC. The Dsalt of anodic sludge reached 31.63 ± 1.26% after 200-day operation, and the removal of organic matter was up to 32.70 ± 1.67%. The Pmax (1.97 ± 0.33 W m−3) was produced on 52 d with open circuit voltage (OCV) of 0.998 ± 0.011 V. After bioelectrochemical stabilization, the feasibility of dehydrated sludge land application was improved. Specifically, the dehydrated sludge humication level significantly enhanced, the contents of available nitrogen, phosphorus and potassium all increased, the heavy metals and metalloids in dehydrated sludge transferred into stable residual form, and phytotoxicity of dehydrated sludge decreased. BES as a pretreatment of dehydrated sludge composting has great potentials.

Microbial Community Characteristics of Shortcut Nitrification Start-up in Different MBR-Inoculated Sludges

In order to clarify the microbial community characteristics of the shortcut nitrification start-up with different inoculated sludges in the membrane bioreactor (MBR), the MBR was inoculated with nitrification sludge (R1), anaerobic nitrification sludge (R2) and 1:1 mixed inoculated anaerobic nitrification and denitrification sludge (R3). The results showed that the combination of intermittent aeration and shortened hydraulic retention time (HRT) successfully achieved the shortcut nitrification by R1, R2 and R3 reactors after 46 d, 8 d and 30 d respectively, with the R2 reactor exhibiting the shortest start-up period. During stable operations, the average nitrite accumulation rates of R1, R2 and R3 reactors were 92%, 93% and 94% respectively, and the R3 reactor showed a more stable shortcut nitrification. The results of analyses using ACE, Chao, Shannon, and Simpson diversity indices showed that the microbial abundance and diversity levels of R1 and R2 were significantly lower than that of the inoculant during the stable operation period, while the species abundance in the R3 reactor was slightly reduced and the diversity level was slightly changed. The main bacteria in the three reactors were Proteobacteria and Bacteroidetes after the successful start-up of shortcut nitrification, and the relative abundance of Proteobacteria was increased compared with the inoculated sludge. Proteobacteria were the main denitrifying bacteria, with β-Proteobacteria being the dominant bacteria of the shortcut nitrification system in the three reactors, accounting for 59.6%, 63.6% and 69.3% respectively. Through further analysis, the next dominant bacteria in R1, R2 and R3 were all Nitrosomonas, with 12.8%, 20.2% and 19.7% respectively. Compared with the R1 reactor, there was a certain proportion of shortcut nitrification bacteria in the sludge of the R2 and R3 reactors, which was more favorable to the operation of the shortcut nitrification system.

Performance and microbial community in a combined VF-HF system for the advanced treatment of secondary effluent.

In this study, a laboratory-scale system combined a vertical flow constructed wetland (VF) with a horizontal flow constructed wetland (HF), which was used to treat the secondary effluent of a wastewater treatment plant. Removal efficiencies of 67.02%, 89.80%, 90.31% and 75.38% were achieved by the system for chemical oxygen demand (COD), ammonium nitrogen (NH4 +-N), total nitrogen (TN) and total phosphorus (TP), respectively. The VF showed much higher average loading rates of COD, TP, NH4 +-N and TN (7.96 g/m2/d, 0.076 g/m2/d, 0.31 g/m2/d and 0.99 g/m2/d) than in HF (0.65 g/m2/d, 0.016 g/m2/d, 0.25 g/m2/d and 0.50 g/m2/d), during the stable operation period. Biodegradation played a major role in pollutant removal, especially for COD and TN. The results of bacterial community analysis indicated that heterotrophic denitrifying bacteria (Hydrogenophaga and Flavobacterium) were the dominant contributors for nitrogen removal in the VF, while heterotrophic denitrifying bacteria (Rhodobacter, Flavobacterium and Dechloromonas) and the autotrophic denitrifying bacteria Sulfurimonas played the principal roles for nitrogen removal in the HF. Redundancy analyses showed that COD and NH4 +-N were the important factors affecting the distribution of nitrogen removal bacteria in the VF, while pH, dissolved oxygen and oxidation-reduction potential were the key factors influencing the distribution of nitrogen removal bacteria in the HF.